This invention relates to apparatus for starting and then operating high-pressure sodium discharge lamps and, more particularly, to such apparatus which provides high-voltage pulses for initiating the discharge in such lamps.
A number of high-pressure sodium discharge lamp lighting circuits have been developed in recent years such as that disclosed in U.S. Pat. No. 4,072,878, issued Feb. 7, 1978, to Engel et al. The Engel patent discloses an apparatus that provides for high-voltage pulses for starting a sodium discharge lamp by using the breakdown characteristics of a Zener diode to provide accurately timed starting pulses. The use of the Zener diode eliminates timing problems encountered when the breakdown characteristics of a glow lamp are used in somewhat similar fashion, as described in U.S. Pat. No. 3,917,976, issued Nov. 4,1975, to Nuckolls, and U.S. Pat. No. 3,963,958, issued June 5, 1976, to Nuckolls.
Another apparatus for starting and operating a high-pressure sodium lamp is disclosed in U.S. Pat. No. 4,143,304, issued Mar. 6, 1979, to Hitchcock et al. The Hitchcock apparatus uses a voltage amplification circuit, utilizing two individual capacitors, the output of which is applied across the ballast reactor which is connected to the reactor in autotransformer relationship. This circuit provides a sufficiently high-voltage starting pulse, even when ballast reactors of low open circuit voltage are used to initiate the operation of high-pressure sodium discharge lamps. Although the Hitchcock circuit works well, it does require a relatively large number of circuit components.